Photochemical processes have been used for treatment of waste waters and groundwaters contaminated with organic chemicals. Photochemical decontamination processes, however, have almost exclusively been based on oxidative reactions initiated by very reactive radicals such as the oxidizing OH radical or by direct photolytic destruction of the contaminant.
Some organic contaminants such as chlorinated organics are refractory to this treatment and degrade very slowly under such oxidative conditions.
When water is subjected to irradiation with high-energy electrons, both oxidizing (.multidot.OH) and reducing radicals are formed [Cooper et al., (1990) in Proceedings of a Symposium on Advanced Oxidation Processes for the Treatment of Contaminated Water and Air, at p.4]. The principal reducing radical produced by radiolysis of water is the aqueous or hydrated electron, e.sup.-.sub.aq.
It is known that hydrated electrons produced by radiolysis react with a variety of organic compounds, including chloroalkanes and chloroalkenes (J.W.T. Spinks and R.J. Woods, "An Introduction to Radiation Chemistry", 3rd Edition: 1990). The use of gamma or electron irradiation has been suggested for degradation of chlorinated organic pollutants [Getoff (1989) Appl. Radiat. Isot., Volume 40, pp. 585-594; (1991) Radiat. Phys. Chem. Volume 37, pp. 673-680], but was found to be less effective than oxidative photochemical processes. In addition, use of gamma or electron irradiation to generate hydrated electrons requires access to an electron accelerator or comparable elaborate equipment.
It has been known for many years that hydrated electrons can be generated by the ultraviolet (UV) photolysis of a number of negatively charged ions, including iodide, I.sup.-. Studies have been made of the reaction of photochemically generated hydrated electrons with chloroalkanes, largely as a tool for determining the nature of the reducing species and the mechanism of the photolysis [Dainton et al., (1965) Proc. Roy Soc. (London) Volume A287, pp. 281-294; Logan et al., (1974) Int. J. Radiat. Phys. Comm., Volume 6, pp. 1--13].
There have been suggestions for employing iodide photolysis and hydrated electron generation as a treatment strategy but these have focused on oxidative hydroxyl radicals as the prime decontamination agent and involved the addition of N.sub.2 O to convert the hydrated electrons to the oxidizing hydroxyl species. The fate of the chloroalkanes was not determined in these studies [Logan and Wilmot (1974) Int. J. Radiat. Phys. Chem., Volume 6, p. 1].
The processes suggested in the literature do not provide for the harnessing of the reductive power of the hydrated electron in a convenient photolysis-based decontamination process.